This invention relates to a vehicle such as a rough terrain forklift, and more particularly to a stabilizing system for the suspension of a rough terrain forklift.
A rough terrain forklift typically has a three-point stance which includes the two front tires and a fulcrum or pivot point provided by a pin-type pivoting connection between the rear of the vehicle frame and the rear axle. This arrangement allows oscillation between the rear axle and the frame during movement of the vehicle over rough terrain. With such an arrangement, it is desirable to provide a system which improves the driving feel of the machine, and which also enhances the stability of the machine beyond industry requirements.
Accordingly, it is an object of the invention to provide a device which improves the handling and feel of a machine such as a rough terrain forklift during operation over rough terrain. It is a further object of the invention to provide a stabilizing system capable of providing varying degrees of damping of oscillation between the vehicle frame and the rear axle. It is yet another object of the invention to vary the degree of damping provided by the stabilizing system in response to an operating condition of the vehicle, such as the position of the forklift boom, relative to the frame.
In accordance with one aspect of the invention, a rough terrain forklift or the like is provided with a frame, a movable member mounted to the frame, and an axle assembly having a pair of wheels for supporting the frame above the ground, with the axle assembly being pivotably mounted to the frame. Damping means is interposed between the axle assembly and the frame for damping oscillation therebetween, with the damping means including means for varying the degree of damping provided thereby in response to the position of the movable member relative to the frame. The movable member may comprise a boom mounted for movement in a substantially vertical plane relative to the frame. The damping means preferably comprises a cylinder; a piston mounted for reciprocating movement within the cylinder, with the cylinder and the piston being connected one to the frame and the other to the axle assembly; and means for providing fluid communication between an area on one side of the piston and an area on the other side of the piston to allow fluid flow therebetween in response to movement of the piston within the cylinder. Variable restricting means as associated with the fluid communication means for restricting the flow of fluid from one side of the piston to the other. The variable restricting means is responsive to the position of the boom relative to the frame for varying the restriction of fluid flow provided thereby. The variable restricting means preferably comprises two or more restricting orifices associated with the fluid communication means, and valve means responsive to the position of the boom for routing fluid through a selected one of the restricting orifices. In one embodiment, the valve means is movable in response to angle-sensitive limit switches mounted to the boom, which selectively move the valve means to one position or another depending on the boom angle for routing fluid through a desired restricting orifice.
The invention also contemplates a method of varying the degree of damping provided by a stabilizing assembly including a damping system, substantially in accordance with the foregoing description.
In accordance with another aspect of the invention, lockout means is provided for selectively incapacitating the damping means. The lockout means is preferably responsive to the position of the boom relative to the frame, for eliminating the effect of the stabilizing system described above and providing a rigid connection between the frame and the axle assembly. In the embodiment in which the stabilizing system employs a cylinder and a piston having a piston rod extending therefrom, the lockout means cuts off communication between the areas of the cylinder on either side of the piston, for preventing movement of the piston within the cylinder. When this occurs, a two-point connection of the rear axle to the frame is attained, thus preventing oscillation between the frame and the rear axle assembly.